TWI852207B - Optical laminate, backlight unit, liquid crystal display device, information device and method for manufacturing backlight unit - Google Patents

Abstract

The present invention aims to provide an optical lamination, a backlight unit, a liquid crystal display device, an information device, and a method for manufacturing a backlight unit. Even if the backlight unit is thinned, the reduction in the uniformity of the brightness within the surface can be suppressed. The optical lamination 100 is assembled in the backlight unit 40. The optical lamination 100 includes: a plurality of diffusion sheets 43 having a plurality of slightly inverted quadrangular pyramid-shaped recesses 22 on a first surface 21a, a pair of prism sheets 44 and a prism sheet 45 laminated on the plurality of diffusion sheets 43 and having prism extension directions orthogonal to each other. The top angle of the recess 22 is greater than 95°. The recesses 22 are arranged in a two-dimensional matrix. The prism extending direction of the lower prism sheet 44 and the arrangement direction of the recessed portions 22 of the upper diffusion sheet 43A intersect with each other at an angle difference within 30°.

Description

Optical laminate, backlight unit, liquid crystal display device, information device and method for manufacturing backlight unit

The present invention relates to an optical laminate, a backlight unit, a liquid crystal display device, an information device, and a method for manufacturing the backlight unit.

Liquid crystal display devices (hereinafter referred to as LCDs) are widely used in display devices of various information devices such as smart phones and tablet terminals. The mainstream backlight of LCDs is the direct-down type in which the light source is arranged on the back of the LCD panel.

In the case of direct backlight, in order to diffuse the light from light sources such as LED (Light Emitting Diode) and improve the uniformity of the overall brightness and color of the screen, optical sheets such as diffusion sheets and prism sheets are used (for example, refer to Patent Document 1). In direct backlight units, two prism sheets with mutually orthogonal prism ridges are usually arranged on the upper side of the diffusion sheet (display screen side). In order to improve the brightness uniformity within the display screen (in-plane brightness uniformity), multiple diffusion sheets are sometimes used in layers.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 2011-129277.

As for backlight units, with the demand for thinner design, it is expected to reduce the thickness of the diffusion sheet and the number of layers. As for direct-type backlight units, since the light source is placed below the display screen, it is also required to reduce the distance between the light source and the diffusion sheet.

However, reducing the thickness of the diffuser sheet or the number of layers, or reducing the distance between the light source and the diffuser sheet to achieve thinning will reduce the uniformity of brightness within the surface.

The purpose of the present invention is to suppress the reduction of the uniformity of brightness within the surface even if the backlight unit is made thinner.

In order to achieve the above-mentioned purpose, the optical sheet laminated body involved in the present invention is assembled in a backlight unit, including a plurality of diffusion sheets and a pair of prism sheets, the plurality of diffusion sheets are provided with a plurality of slightly inverted quadrangular pyramid-shaped recesses on at least one side, the pair of prism sheets are laminated on the plurality of diffusion sheets, and the prism extension directions are mutually orthogonal, the top angles of the plurality of recesses are greater than 95°, the plurality of recesses are arranged in a two-dimensional matrix, and the prism extension direction of the lower prism sheet close to the plurality of diffusion sheets in the pair of prism sheets and the arrangement direction of the plurality of recesses of the upper diffusion sheet closest to the lower prism sheet in the plurality of diffusion sheets intersect with an angle difference within 30°.

According to the optical sheet stacking body involved in the present invention, when compared with the same light source and the same optical sheet stacking structure, the in-plane brightness uniformity can be significantly increased compared with the case where the top angle of the slightly inverted quadrangular pyramidal concave portion in each diffusion sheet is less than 95° and the angle difference between the arrangement direction of the concave portion of the upper diffusion sheet and the prism extension direction of the lower prism sheet exceeds 30°. Therefore, even if the backlight unit is thinned by reducing the thickness of the diffusion sheet or the number of stacking sheets, the reduction in in-plane brightness uniformity can be suppressed.

As for the optical sheet laminate involved in the present invention, if the aforementioned top angle is less than 120°, and more preferably less than 110°, the reduction of the light diffusion effect caused by the plurality of concave portions can be suppressed.

As for the optical sheet laminate involved in the present invention, if there is no other optical sheet between the upper diffusion sheet and the lower prism sheet, the reduction of optical characteristics such as in-plane brightness uniformity caused by the other optical sheets can be suppressed.

As for the optical sheet laminate involved in the present invention, if the aforementioned plurality of recesses are arranged on the light-emitting surface of the aforementioned upper diffusion sheet opposite to the aforementioned lower prism sheet, the uniformity of brightness within the surface can be increased compared to the case where the recesses are arranged on the light-incident surface.

In the optical sheet laminate of the present invention, if the plurality of diffusion sheets include a lower diffusion sheet whose arrangement direction of the plurality of concave portions is different from that of the upper diffusion sheet, then by adjusting the intersection angle between the arrangement direction of the concave portions of the upper diffusion sheet and the arrangement direction of the concave portions of the lower diffusion sheet, for example, a balance between the uniformity of brightness within the surface and the brightness can be achieved.

The backlight unit involved in the present invention is assembled in a liquid crystal display device, and guides light emitted from a plurality of point light sources toward the display screen side. The optical sheet layer involved in the present invention is included between the display screen and the plurality of point light sources, and the plurality of diffusion sheets are arranged between the plurality of point light sources and the pair of prism sheets.

According to the backlight unit involved in the present invention, including the optical sheet layer involved in the present invention, the reduction of the uniformity of brightness within the surface can be suppressed even for thinning.

As for the backlight unit involved in the present invention, if the aforementioned multiple point light sources are white light sources, there is no need to set a color conversion sheet, so it is easy to achieve thinness.

In the backlight unit involved in the present invention, the plurality of point light sources can be arranged on a reflective sheet disposed on the opposite side of the display screen from the plurality of diffusion sheets. In this way, the light is further diffused by multiple reflections between the diffusion sheet and the reflective sheet, thereby further improving the uniformity of the brightness within the surface.

As for the backlight unit involved in the present invention, the distance between the plurality of point light sources and the diffusion sheet can be less than 5 mm, preferably less than 2.5 mm, and even more preferably less than 1 mm. In this way, thinness can be achieved.

The liquid crystal display device involved in the present invention includes the backlight unit and the liquid crystal display panel involved in the aforementioned present invention.

According to the liquid crystal display device involved in the present invention, including the backlight unit involved in the above-mentioned present invention, it is possible to suppress the reduction of the uniformity of brightness within the surface even when thinning.

The information device involved in the present invention includes the liquid crystal display device involved in the aforementioned present invention.

According to the information device involved in the present invention, including the liquid crystal display device involved in the present invention, the reduction in the uniformity of brightness within the surface can be suppressed even for thinning.

The manufacturing method of the backlight unit involved in the present invention is a manufacturing method of the backlight unit which is assembled in a liquid crystal display device and guides light emitted from a plurality of point light sources toward the display screen side. The manufacturing method of the backlight unit involved in the present invention includes the following steps: a step of arranging a plurality of diffusion sheets by lamination on the display screen side when observed from the plurality of point light sources, the plurality of diffusion sheets having a plurality of slightly inverted quadrangular pyramid-shaped recesses on at least one side; a step of arranging a pair of prism sheets whose prism extension directions are orthogonal to each other on the display screen side when observed from the plurality of diffusion sheets; the plurality of recesses have a top angle of 95° or more, and the plurality of recesses are arranged in a two-dimensional matrix. The plurality of diffusion sheets and the pair of prism sheets are arranged so that the prism extension direction of the lower prism sheet in the pair of prism sheets close to the plurality of diffusion sheets intersects with the arrangement direction of the plurality of recesses of the upper diffusion sheet closest to the lower prism sheet in the plurality of diffusion sheets with an angle difference within 30°.

According to the manufacturing method of the backlight unit involved in the present invention, when the same light source and the same optical sheet stacking structure are compared, the in-plane brightness uniformity can be significantly increased compared with the case where the top angle of the slightly inverted quadrangular pyramidal concave portion in each diffusion sheet is less than 95° and the angle difference between the arrangement direction of the concave portion of the upper diffusion sheet and the prism extension direction of the lower prism sheet exceeds 30°. Therefore, even if the backlight unit is thinned by reducing the thickness of the diffusion sheet or the number of stacking sheets, the reduction in in-plane brightness uniformity can be suppressed.

According to the present invention, even if the backlight unit is made thinner, the reduction in the uniformity of the brightness within the surface can be suppressed.

1: TFT substrate

2:CF substrate

3: Liquid crystal layer

5: LCD panel

6: First polarizing plate

7: Second polarizing plate

21: Base material layer

21a: Page 1

21b: Second side

22: Concave part

40: Backlight module

41: Reflective sheet

42: Point light source

43: Diffusion film

43A: Upper diffusion sheet

43B: Lower diffusion piece

44: Lower prism lens

44a: base material layer

44b: protruding prism part

45: Upper prism lens

45a: base material layer

45b: protruding prism part

50: LCD display device

50a: Display screen

100: Optical sheet layer

111: Ridge

112: Center of concave part (apex of inverted pyramid)

[Figure 1] is a cross-sectional view of a liquid crystal display device including a backlight unit involved in an implementation form.

[Figure 2] is a cross-sectional view of a backlight unit assembled with an optical sheet layer according to an embodiment.

[Figure 3] is a cross-sectional view of a diffusion sheet included in an optical sheet layer according to an embodiment.

[Figure 4] is a three-dimensional diagram of the diffusion sheet included in the optical sheet layer involved in the implementation form.

[Figure 5] is a diagram showing the planar structure and cross-sectional structure of a recessed portion provided on one surface of a diffusion sheet, and the optical sheet laminate according to the embodiment includes the diffusion sheet.

[Figure 6] is a diagram showing an example of the relationship between the concave arrangement direction of the upper diffusion sheet and the prism extension direction of the lower prism sheet in the optical sheet laminate according to the embodiment.

[Figure 7] is a diagram illustrating the arrangement angles of the diffusion sheet and the prism sheet in the optical sheet laminate according to the embodiment.

[Figure 8] is a diagram showing the change in brightness when the configuration angle of all diffusion sheets is changed in the optical sheet laminate according to the embodiment.

[Figure 9] is a diagram showing the change in brightness uniformity when the configuration angle of all diffusion sheets is changed in the optical sheet laminate according to the embodiment.

[Figure 10] is a diagram showing the change in brightness when the configuration angle of the upper diffusion sheet is changed in the optical sheet laminate according to the embodiment.

[Figure 11] is a diagram showing the change in brightness uniformity when the configuration angle of the upper diffusion sheet is changed in the optical sheet laminate according to the embodiment.

Below, the optical lamination, backlight unit, liquid crystal display device, information device and manufacturing method of the backlight unit involved in the implementation form are described with reference to the drawings. It should be noted that the scope of the present invention is not limited to the following implementation forms and can be arbitrarily changed within the scope of the technical concept of the present invention.

[Structure of liquid crystal display device]

As shown in FIG1 , the liquid crystal display device 50 includes a liquid crystal display panel 5, a first polarizing plate 6 attached to the lower surface of the liquid crystal display panel 5, a second polarizing plate 7 attached to the upper surface of the liquid crystal display panel 5, and a backlight unit 40 disposed on the back side of the liquid crystal display panel 5 via the first polarizing plate 6.

The liquid crystal display panel 5 includes a TFT substrate 1 and a CF substrate 2 disposed opposite to each other, a liquid crystal layer 3 disposed between the TFT substrate 1 and the CF substrate 2, and a sealing material (not shown) disposed in a frame shape to seal the liquid crystal layer 3 between the TFT substrate 1 and the CF substrate 2.

The shape of the display screen 50a of the liquid crystal display device 50 viewed from the surface (the top of FIG. 1 ) is in principle a rectangle or a square, but is not limited thereto and can be any shape such as a rectangle with rounded corners, an ellipse, a circle, a trapezoid, or a car dashboard.

In each sub-pixel corresponding to each pixel electrode of the liquid crystal display device 50, a voltage of a predetermined magnitude is applied to the liquid crystal layer 3 to change the alignment state of the liquid crystal layer 3. Thus, the transmittance of the light incident from the backlight unit 40 through the first polarizer 6 is adjusted. The light with adjusted transmittance is emitted through the second polarizer 7 to display an image.

The liquid crystal display device 50 of this embodiment can be used as a display device assembled in various information devices (for example, vehicle-mounted devices such as car navigation, portable information terminal devices such as personal computers, mobile phones, notebook computers or tablet computers, portable game consoles, copiers, ticket machines, ATMs, etc.).

The TFT substrate 1 includes, for example, a plurality of TFTs arranged in a matrix on a glass substrate, an interlayer insulating film provided to cover each TFT, a plurality of pixel electrodes arranged in a matrix on the interlayer insulating film and connected to corresponding TFTs among the plurality of TFTs, and an alignment film provided to cover each pixel electrode. The CF substrate 2 includes, for example, a black matrix arranged in a grid on a glass substrate, a color filter including a red layer, a green layer, and a blue layer respectively provided between each grid of the black matrix, a common electrode provided to cover the black matrix and the color filter, and an alignment film provided to cover the common electrode. The liquid crystal layer 3 is formed by a nematic liquid crystal material, etc., which contains liquid crystal molecules with electro-optical properties. The first polarizing plate 6 and the second polarizing plate 7, for example, both include: a polarizing film layer with a unidirectional polarization axis, and a pair of protective layers arranged in a manner of sandwiching the polarizing film layer.

[The composition of the backlight unit and optical layer]

As shown in FIG. 2 , the backlight unit 40 includes: a reflective sheet 41; a plurality of point light sources 42 arranged in a two-dimensional shape on the reflective sheet 41; and an optical sheet layer 100 disposed on the upper side of the plurality of point light sources 42. The optical sheet layer 100 has a plurality of diffusion sheets 43 disposed on the side of the point light sources 42 and a pair of prism sheets 44 and a prism sheet 45 disposed on the upper side (display screen 50a side) of the plurality of diffusion sheets 43. Any sheet in the optical sheet layer 100 may be spaced apart. In this case, an air layer may exist between the spaced sheets.

In this embodiment, two diffusion sheets 43 of the same structure are stacked in the backlight unit 40. Specifically, an upper diffusion sheet 43A and a lower diffusion sheet 43B are provided as the diffusion sheet 43. The upper diffusion sheet 43A is arranged on a side close to the prism sheet 44 and the prism sheet 45, and the lower diffusion sheet 43B is arranged on a side close to the point light source 42. The diffusion sheet 43 may be stacked in three or more sheets. It should be noted that, in the case where the brightness uniformity can be sufficiently ensured by the precise arrangement of the point light source 42 of the backlight unit 40, a single diffusion sheet 43 may be used. A pair of prisms 44 and 45 may be a lower prism 44 and an upper prism 45 whose prism extension directions (extension directions of prism ridges) are orthogonal to each other. Although not shown in the figure, a polarizer may be provided on the upper side (display screen 50a side) of the prisms 44 and 45. The polarizer improves the brightness of the display screen 50a by preventing the light emitted from the backlight unit 40 from being absorbed by the first polarizer 6 of the liquid crystal display device 50.

The reflective sheet 41 is made of, for example, a white polyethylene terephthalate resin film, a silver vapor-deposited film, etc.

There is no particular limitation on the type of point light source 42, and for example, it can be an LED element or a laser element. From the perspective of cost and productivity, LED elements can be used. In order to adjust the light emission angle characteristics of the LED element, a lens can be installed on the LED element. The plurality of point light sources 42 can be, for example, a white light source, which emits light in the chromaticity coordinates of 0.24<x<0.42 and 0.18<y<0.48 of CIE1931. Specifically, the plurality of point light sources 42 can be composed of LED elements with a peak wavelength in the blue region, LED elements with a peak wavelength in the green region, and LED elements with a peak wavelength in the red region. When viewed from above, the LED elements (chips) of various colors constituting the plurality of point light sources 42 may be rectangular, in which case the length of one side may be greater than 10 μm (preferably greater than 50 μm) and less than 5 mm (preferably less than 1 mm). The LED chips corresponding to each color may also be arranged two-dimensionally on the reflector 41 alternately at a certain interval. The center distance between two adjacent LED chips may be greater than 0.5 mm (preferably greater than 2 mm) and less than 20 mm.

As shown in FIG3 , the diffusion sheet 43 has a base layer 21. The diffusion sheet 43 has a first surface 21a that is a light emitting surface and a second surface 21b that is a light incident surface. That is, the second surface 21b of the diffusion sheet 43 is arranged to face the point light source 42. The base layer 21 is not particularly limited as long as it is formed of a resin material that allows light to pass through. For example, acrylate, polystyrene, polycarbonate, MS (methyl methacrylate/styrene copolymer) resin, polyethylene terephthalate, polyethylene naphthalate, cellulose acetate, polyimide, etc. can be used. The base layer 21 may contain a diffuser and other additives, or may substantially contain no additives. The additives that the substrate layer 21 may contain are not particularly limited, and may be inorganic particles such as silicon dioxide, titanium oxide, aluminum hydroxide, and barium sulfate, or organic particles such as acrylate, acrylonitrile, polysilicone, polystyrene, and polyamide.

The thickness of each diffusion sheet 43 is not particularly limited, and can be, for example, less than 1 mm and greater than 0.05 mm. If the thickness of the diffusion sheet 43 is less than 1 mm, the backlight unit 40 can be thinned. If the thickness of the diffusion sheet 43 is greater than 0.05 mm, it is easy to obtain a sufficient light diffusion effect. Each diffusion sheet 43 can be in the form of a film or a sheet (plate).

As shown in FIG4 , on the first surface 21a of the diffusion sheet 43, a plurality of recesses 22 in a slightly inverted quadrangular pyramid shape (inverted pyramid shape) are arranged in a two-dimensional matrix shape. In other words, a plurality of recesses 22 are arranged along two directions that are orthogonal to each other. Adjacent recesses 22 are separated from each other by ridges 111. The ridges 111 extend along the two directions in which the recesses 22 are arranged. The center (vertex of the inverted pyramid) 112 of the recess 22 is the deepest part of the recess 22. For simplicity of representation, FIG4 illustrates an example in which the recesses 22 are arranged in a 5×5 matrix shape, but the actual number of arrangements of the recesses 22 is much greater than that shown. In the two-dimensional arrangement of the recesses 22, each recess 22 can be arranged without gaps on the first surface 21a, or can be arranged at a specified interval. It is also possible to randomly arrange some of the recesses 22 to a degree that does not destroy the light diffusion effect. The arrangement pitch p of the recesses 22 (see FIG. 3 ) can be, for example, 100 μm, and the depth of the recesses 22 can be, for example, 50 μm.

In the optical sheet laminate 100 of the present embodiment, the vertex angle θ of the recess 22 (see FIG. 3 ) is set to be greater than 95°. It should be noted that, in order to suppress the reduction of light diffusivity caused by the diffusion sheet 43, the upper limit of the vertex angle θ of the recess 22 may be set to, for example, 120° (preferably 110°). Here, as shown in FIG. 5 , the vertex angle θ of the recess 105 is the angle defined by the angle between the inclined surfaces of the recess 22 in a plane (longitudinal section) perpendicular to the mounting surface (horizontal plane) of the diffusion sheet 43, in a cross section (lower figure of FIG. 5 ) formed when the recess 22 is cut in a perpendicular manner through a pair of ridges 111 that are opposite to each other and sandwich the vertex 112, passing through the vertex 112 of the inverted pyramid. It should be noted that the upper figure of FIG. 5 shows the planar structure of the concave portion 22. In FIG. 5, "H" represents the depth of the concave portion 22 (the height of the inverted pyramid), and "P" represents the horizontal width of the concave portion 22, that is, the arrangement pitch when the concave portions 22 are arranged without gaps. The depth H of the concave portion 22 is determined by the arrangement pitch P of the concave portion 22 and the top angle θ.

The second surface (light incident surface) 21b of each diffusion sheet 43 can be, for example, a plane (mirror surface) or an embossed surface. Each diffusion sheet 43 can be composed of a single-layer structure of a substrate layer 21 having a concave-convex shape (concave portion 22) on the first surface (light exit surface) 21a. Each diffusion sheet 43 can also be composed of a double-layer structure of a substrate layer with two flat surfaces and a layer with a concave-convex shape on one surface. Each diffusion sheet 43 can also be composed of a structure including three or more layers with a concave-convex shape on one surface. The manufacturing method of each diffusion sheet 43 is not particularly limited, and for example, extrusion molding, injection molding, etc. can be used.

The steps for manufacturing a single-layer diffusion sheet with a concave-convex shape on the surface using the extrusion molding method are as follows. First, granular plastic particles (diffusers may be added) are placed in a single-screw extruder, heated, melted, and kneaded. After that, the molten resin extruded from the T-die is clamped by two metal rollers and cooled, then transported by guide rollers and cut into single flat plates by a slicer to produce a diffusion sheet. Here, by clamping the molten resin with a metal roller whose surface shape is opposite to the desired concave-convex shape, the opposite shape of the roller surface is transferred to the resin, so that the desired concave-convex shape can be given to the surface of the diffusion sheet. Because the shape of the roller surface may not be 100% transferred to the resin, the shape of the roller surface can be designed by reverse calculation based on the degree of transfer.

When using the extrusion molding method to manufacture a double-layer structure with a concave-convex shape on the surface of a diffusion sheet, for example, after the granular plastic particles required to form each layer are respectively put into two single-screw extruders, the same steps as above are implemented for each layer, and the sheets are stacked to produce each layer.

Alternatively, a diffusion sheet with a double-layer structure having a concavo-convex shape on the surface can be produced as described below. First, the granular plastic particles required to form each layer are respectively put into two single-screw extruders, and melted and kneaded while heating. After that, the molten resin forming each layer is put into a T-die, and the layered molten resin extruded from the T-die is clamped by two metal rollers for cooling. After that, the layered molten resin is transported by a guide roller and cut into a single flat plate by a slicer, thereby producing a diffusion sheet with a double-layer structure having a concavo-convex shape on the surface.

You can also use UV (ultraviolet) shaping transfer to make a diffusion sheet as follows. First, fill an uncured UV curing resin on a roller that has the opposite shape of the concave and convex shape to be transferred, and then press the substrate onto the resin. Then, while the roller filled with the UV curing resin and the substrate are integrated, irradiate the resin with ultraviolet light to cure it. Then, peel off the sheet with the concave and convex shape transferred by the resin shaping transfer from the roller. Finally, irradiate the sheet with ultraviolet light again to completely cure the resin, thereby making a diffusion sheet with a concave and convex shape on the surface.

It should be noted that in the present invention, the expression "slightly inverted pyramid" is used, considering that it is difficult to form a concave part of an inverted pyramid strictly defined in geometry by ordinary shape transfer technology, but "slightly inverted pyramid" of course also includes a shape that is truly or substantially an inverted pyramid. "Slightly" means that it can be approximated, and "slightly inverted pyramid" means a shape that can be approximated to an inverted pyramid. For example, for an "inverted pyramid trapezoid" with a flat top, a shape with a small top area to the extent that the function and effect of the present invention are not lost is also included in the "slightly inverted pyramid". Shapes deformed from an "inverted pyramid" within the range of inevitable shape deviation caused by processing accuracy in industrial production are also included in the "slightly inverted pyramid".

Since it is necessary to allow light to pass through, the prism sheet 44 and the prism sheet 45 are formed of a transparent (e.g., colorless and transparent) synthetic resin as a main component. The prism sheet 44 and the prism sheet 45 can be formed as a whole. The lower prism sheet 44 has a protrusion row consisting of a base layer 44a and a plurality of protrusion prism portions 44b stacked on the surface of the base layer 44a. Similarly, the upper prism sheet 45 has a base layer 45a and a protrusion row consisting of a plurality of protrusion prism portions 45b stacked on the surface of the base layer 45a. The protruding prism portion 44b and the protruding prism portion 45b are respectively laminated in stripes on the surfaces of the substrate layer 44a and the substrate layer 45a. The protruding prism portion 44b and the protruding prism portion 45b are triangular prisms whose back surfaces are connected to the surfaces of the substrate layer 44a and the substrate layer 45a, respectively. The extension direction of the protruding prism portion 44b and the extension direction of the protruding prism portion 45b are orthogonal to each other. In this way, the light incident from the light diffusion sheet 43 can be refracted laterally in the normal direction by the lower prism sheet 44, and the light emitted from the lower prism sheet 44 can be refracted by the upper prism sheet 45 in a manner that is approximately perpendicular to the display screen 50a.

The lower limit of the thickness of the prism sheet 44 and the prism sheet 45 (the height from the back surface of the substrate layer 44a and the substrate layer 45a to the apex of the protruding prism portion 44b and the protruding prism portion 45b) is, for example, about 50 μm, and more preferably about 100 μm. On the other hand, the upper limit of the thickness of the prism sheet 44 and the prism sheet 45 is about 200 μm, and more preferably about 180 μm. The lower limit of the distance between the protruding prism portion 44b and the protruding prism portion 45b in the prism sheet 44 and the prism sheet 45 is, for example, about 20 μm, and more preferably about 25 μm. The upper limit of the distance between the protruding prism parts 44b and 45b in the prism pieces 44 and 45 is, for example, about 100 μm, and more preferably about 60 μm. The top angle of the protruding prism parts 44b and 45b can be, for example, greater than 85° and less than 95°. The lower limit of the refractive index of the protruding prism parts 44b and 45b is, for example, 1.5, and more preferably 1.55. The upper limit of the refractive index of the protruding prism parts 44b and 45b can be, for example, 1.7.

The prism sheets 44 and 45 may be, for example, substrate layers 44a and 45a formed of PET (polyethylene terephthalate) films, on which protruding prism portions 44b and 45b are transferred in shape using UV-curable acrylic resin, or the protruding prism portions 44b and 45b are integrally formed with the substrate layers 44a and 45a.

In the optical sheet laminate 100 of the present embodiment, for example, as shown in FIG6 , the extension direction of the protruding prism portion 44b in the lower prism sheet 44 (hereinafter also referred to as the prism extension direction) intersects with the arrangement direction of the plurality of recesses 22 in the upper diffusion sheet 43A (the X direction and the Y direction shown in FIG6 : hereinafter also referred to as the recess arrangement direction) at an angle difference within 30°.

[Characteristics of implementation form]

The optical sheet laminate 100 of this embodiment includes: a plurality of diffusion sheets 43 having a plurality of slightly inverted quadrangular pyramid-shaped recesses 22 on the first surface 21a, and a pair of prism sheets 44 and prism sheets 45 whose prism extension directions are orthogonal to each other. The top angle of the plurality of recesses 22 is greater than 95°, and the plurality of recesses 22 are arranged in a two-dimensional matrix. The recess arrangement direction of the upper diffusion sheet 43A among the plurality of diffusion sheets 43 intersects with the prism extension direction of the lower prism sheet 44 at an angle difference of less than 30°.

According to the optical sheet stacking body 100 of this embodiment, when compared with the same light source and the same optical sheet stacking structure, the in-plane brightness uniformity can be significantly increased compared with the case where the top angle of the slightly inverted quadrangular pyramidal recess 22 in each diffusion sheet 43 is less than 95° and the angle difference between the recess arrangement direction of the upper diffusion sheet 43A and the prism extension direction of the lower prism sheet 44 exceeds 30°. Therefore, even if the backlight unit 40 is thinned by reducing the thickness of the diffusion sheet 43 or the number of stacking sheets, the reduction in in-plane brightness uniformity can be suppressed.

For the optical sheet laminate 100 of this embodiment, if the top angle of the recess 22 is less than 120°, and more preferably less than 110°, the reduction in the light diffusion effect caused by the recess 22 can be suppressed.

In the optical sheet laminate 100 of this embodiment, if a plurality of recesses 22 are provided on the light-emitting surface (i.e., the first surface 21a) of the upper diffusion sheet 43A opposite to the lower prism sheet 44, the uniformity of the brightness within the surface can be increased compared to the case where the recesses 22 are provided on the light-incident surface (i.e., the second surface 21b).

In the optical sheet laminate 100 of the present embodiment, the concave arrangement direction of the upper diffusion sheet 43A and the concave arrangement direction of the lower diffusion sheet 43B may also be different. In this way, by adjusting the intersection angle of the concave arrangement directions of the upper diffusion sheet 43A and the lower diffusion sheet 43B, for example, a balance between the brightness uniformity and the brightness within the surface can be achieved.

The backlight unit 40 of this embodiment is assembled in the liquid crystal display device 50, and guides the light emitted from the plurality of point light sources 42 to the side of the display screen 50a. The backlight unit 40 includes the optical sheet layer 100 of this embodiment between the display screen 50a and the plurality of point light sources 42, and the plurality of diffusion sheets 43 are arranged between the plurality of point light sources 42 and the prism sheet 44 and the prism sheet 45.

According to the backlight unit 40 of this embodiment, including the optical sheet laminate 100 of this embodiment, it is possible to suppress the reduction of the uniformity of the brightness within the surface even when the thickness is reduced.

As for the backlight unit 40 of the embodiment, if the plurality of point light sources 42 are white light sources, there is no need to set a color conversion sheet, so it is easy to achieve thinness.

In the backlight unit 40 of this embodiment, a plurality of point light sources 42 can be arranged on a reflective sheet 41 disposed on the opposite side of the display screen 50a from the diffuser sheet 43. In this way, the light is further diffused by multiple reflections between the diffuser sheet 43 and the reflective sheet 41, so that the brightness uniformity is improved.

For the backlight unit 40 of this embodiment, if the distance between the plurality of point light sources 42 and the diffusion sheet 43 is less than 5 mm, the backlight unit 40 can be made thinner. Considering the thinning of small and medium-sized liquid crystal displays in the future, the distance between the point light source 42 and the diffusion sheet 43 is preferably less than 2.5 mm, more preferably less than 1 mm, and can eventually be 0 mm.

The manufacturing method of the backlight unit 40 of the present embodiment includes the following steps: a step of arranging a plurality of diffusion sheets 43 on the display screen 50a side as viewed from the plurality of point light sources 42, wherein the plurality of diffusion sheets 43 are provided with a plurality of recesses 22 in a slightly inverted quadrangular pyramid shape; and a step of arranging a pair of prism sheets 44 and 45 on the display screen 50a side as viewed from the diffusion sheets 43, wherein the prism extension directions are orthogonal to each other. The vertex angles of the plurality of recesses 22 are greater than 95 degrees, and the plurality of recesses 22 are arranged in a two-dimensional matrix. The plurality of diffusion sheets 43 and a pair of prism sheets 44 and prism sheets 45 are arranged so that the prism extension direction of the lower prism sheet 44 and the concave arrangement direction of the upper diffusion sheet 43A intersect with an angle difference within 30°.

According to the manufacturing method of the backlight unit 40 of this embodiment, when compared with the same light source and the same optical sheet stacking structure, the in-plane brightness uniformity can be significantly increased compared with the case where the top angle of the slightly inverted quadrangular pyramid-shaped recess 22 in the diffusion sheet 43 is less than 95° and the angle difference between the recess arrangement direction of the upper diffusion sheet 43A and the prism extension direction of the lower prism sheet 44 exceeds 30°. Therefore, even if the backlight unit 40 is thinned by reducing the thickness of the diffusion sheet 43 or the number of stacked sheets, the reduction in in-plane brightness uniformity can be suppressed.

The liquid crystal display device 50 of this embodiment includes the backlight unit 40 and the liquid crystal display panel 5 of this embodiment, so that the reduction of the uniformity of the brightness within the surface can be suppressed even when the device is thinned. An information device (such as a portable information terminal such as a laptop or tablet computer) equipped with the liquid crystal display device 50 of this embodiment can also obtain the same effect.

(Implementation example)

The following is an explanation of the implementation example.

As an optical sheet laminate 100 of the embodiment, a lower prism sheet 44 and an upper prism sheet 45 whose prism extension directions are orthogonal to each other are arranged on a laminate formed by laminating two diffusion sheets 43 of the same structure and thickness of 130 μm in the same direction (the direction in which the formation surface of the concave portion 22 becomes the light emitting surface).

The polycarbonate used as the substrate layer 21 is processed by extrusion molding, and the inverted pyramid-shaped recesses 22 with a depth of 50μm are arranged two-dimensionally, and the diffusion sheet 43 is formed with a single-layer structure. As the diffusion sheet 43, four types of diffusion sheets are prepared, with the top angles of the recesses 22 being 90° (comparative example), 95°, 100°, and 105° (95° to 105° are examples). The light-entering surface of each diffusion sheet 43 is processed into a matte surface.

The prism sheet 44 and the prism sheet 45 are formed by providing the protruding prism portion 44b and the protruding prism portion 45b on the substrate layer 44a and the substrate layer 45a formed by PET film using UV curing acrylic resin formed by acrylate. The protruding prism portion 44b of the lower prism sheet 44 with a total thickness of 145μm, a height of 12μm, and a top angle of 94° is arranged at a pitch of 25μm. The protruding prism portion 45b of the upper prism sheet 45 with a total thickness of 128μm, a height of 24μm, and a top angle of 93° is arranged at a pitch of 51μm.

A plurality of point light sources 42 as white light sources are arranged on the lower side (the diffuser 43 side) of the optical sheet layer 100 of the embodiment, and the arrangement relationship between the diffuser 43 and the prism 44 and the prism 45 is changed, while analyzing the brightness of the light passing through the optical sheet layer 100 and the uniformity of the brightness within the surface (hereinafter referred to as "brightness uniformity").

Specifically, as the plurality of point light sources 42, a plurality of blue LEDs with a peak wavelength of 456nm (half-height full width 19nm), green LEDs with a peak wavelength of 535nm (half-height full width 53nm), and red LEDs with a peak wavelength of 631nm (half-height full width 10nm) are used, and a plurality of LED arrays are alternately arranged two-dimensionally at a pitch of 8.4mm.

As the initial state of the measurement of brightness and brightness uniformity, as shown in FIG7, each diffusion sheet 43 is arranged so that the arrangement direction of the recessed portion 22 is consistent with the reference direction (X-axis direction) (at a configuration angle of 0°), the lower prism sheet 44 is arranged so that the extension direction of the protruding prism portion 44b is rotated 125° counterclockwise relative to the X-axis (at a configuration angle of 125°), and the upper prism sheet 45 is arranged so that the extension direction of the protruding prism portion 45b is rotated 35° counterclockwise relative to the X-axis (at a configuration angle of 35°). It should be noted that the "reference direction" is consistent with the arrangement direction of the LEDs in the plurality of point light sources 42 (the aforementioned LED array).

In the first measurement, the arrangement direction (arrangement angle) of the two diffusion sheets 43 was rotated counterclockwise by 10° each time from the initial state until it was rotated by 80°, and the brightness and brightness uniformity were measured at each arrangement angle. In the second measurement, the arrangement direction (arrangement angle) of only the upper diffusion sheet 43A was rotated counterclockwise by 10° each time from the initial state until it was rotated by 80°, and the brightness and brightness uniformity were measured at each arrangement angle. It should be noted that when each diffusion sheet 43 is rotated 90° from the initial state, the concave arrangement direction becomes the same as the initial state.

In each measurement, the optical sheet laminate 100 of the embodiment and the comparative example was arranged on a plurality of point light sources 42 (LED array), and a transparent glass plate was placed on the optical sheet laminate 100 to suppress the floating of the sheet. The brightness in the vertical direction upward (from the LED array to the glass plate) was measured for a range of 33 mm square using a two-dimensional spectroradiometer SR-5000HS manufactured by TOPCON TECHNOHOUSE. For the obtained two-dimensional brightness distribution image, the deviation of the light intensity of each LED was corrected, and after filtering processing for suppressing bright/dark spot noise caused by foreign matter, the average value and standard deviation of the brightness of all pixels were calculated. Finally, "in-plane brightness uniformity" was defined as "average brightness/standard deviation of brightness", and the in-plane brightness uniformity of the evaluation samples of the embodiment and the comparative example was calculated.

FIG8 and FIG9 show the change of brightness and brightness uniformity obtained in the aforementioned first measurement relative to the configuration angle (i.e., the rotation angle from the initial state of 0°) of the diffusion sheet 43 (upper diffusion sheet 43A and lower diffusion sheet 43B). FIG10 and FIG11 show the change of brightness and brightness uniformity obtained in the aforementioned second measurement relative to the configuration angle (i.e., the rotation angle from the initial state of 0°) of the upper diffusion sheet 43A. It should be noted that in FIG8 and FIG10, the brightness (average brightness of all pixels) is expressed as the relative brightness of 1 obtained by the first measurement when the rotation angle is 0° in the comparison example where the top angle of the concave portion 22 is 90°.

As shown in Figures 8 and 10, in any of the first and second measurements, the overall brightness of the embodiment (vertex angles of 95°, 100°, 105°) is improved compared to the comparative example (vertex angle of 90°), and the decrease in brightness accompanying the change in the rotation angle is also suppressed.

As shown in Figures 9 and 11, in any of the first and second measurements, the embodiment (vertex angles of 95°, 100°, 105°) has better overall brightness uniformity than the comparative example (vertex angle of 90°). Specifically, in the first measurement (Figure 9), except for the rotation angles of 0° and 80° (the case of the vertex angle of 100°), the brightness uniformity of the embodiment is about 20% higher than that of the comparative example. In the second measurement (Figure 11), except for the rotation angles of 0° (when the top angle is 95° and 105°), 60° (when the top angle is 105°) and 80° (when the top angle is 100° and 105°), the brightness uniformity of the embodiment is about 10% to 20% higher than that of the comparative example.

Here, considering that the configuration angle of the lower prism sheet 44 is 125°, each diffusion sheet 43 has an equivalent shape at the configuration angle of 0° (180°) and 90° (270°), it can be seen that when the prism extension direction of the lower prism sheet 44 and the concave arrangement direction of the upper diffusion sheet 43A intersect with an angle difference within 30° (preferably within 20°), the brightness uniformity of each embodiment is good.

(Other implementation forms)

In the above-mentioned embodiments (including the embodiments, the same below), the optical sheet laminate 100 is composed of the diffuser 43, the prism 44 and the prism 45. However, the optical sheet laminate 100 may further include other optical sheets other than the diffuser 43 and the prism 44 and the prism 45. For example, when a blue light source is used as a plurality of point light sources 42, a color conversion sheet such as a QD (quantum dot; Quantum Dot) sheet, a fluorescent sheet, etc. that converts blue light into white light may be arranged between the plurality of point light sources 42 and the lower diffuser 43B. Alternatively, other optical sheets that do not substantially affect the optical characteristics of the backlight unit 40 may be sandwiched between the upper diffuser 43A and the lower prism 44.

In the above-mentioned embodiment, the concave portion 22 is provided on the first surface (light emitting surface) 21a of all the diffusion sheets 43 included in the optical sheet laminate 100, but instead, the concave portion 22 may be provided on the second surface (light incident surface) 21b of the lower diffusion sheet 43B (when three or more diffusion sheets 43 are laminated, at least one of the diffusion sheets 43 other than the upper diffusion sheet 43A). The second surface 21b of each diffusion sheet 43 is a flat surface (mirror surface) or an embossed surface, but a protrusion row such as an inverted polygonal pyramidal concave portion or a convex prism portion that can be arranged in two dimensions may be provided on the second surface 21b of each diffusion sheet 43. As a plurality of diffusion sheets 43, a plurality of diffusion sheets having different materials of the base layer 21 or structures of the recessed portion 22 may be used.

The above describes the implementation forms of the present invention, but the present invention is not limited to the aforementioned implementation forms, and various changes can be made within the scope of the present invention. That is, the description of the aforementioned implementation forms is only an example in nature, and is not used to limit the present invention, its applicable objects or uses.

Claims (13)

An optical sheet laminate is assembled in a backlight unit, comprising a plurality of diffusion sheets and a pair of prism sheets; the plurality of diffusion sheets are provided with a plurality of slightly inverted quadrangular pyramid-shaped recesses on at least one side; the pair of prism sheets are laminated on the plurality of diffusion sheets, and the prism extension directions are mutually orthogonal; the top angles of the plurality of recesses are greater than 95°; the plurality of recesses are arranged in a two-dimensional matrix; the prism extension direction of the lower prism sheet in the pair of prism sheets close to the plurality of diffusion sheets intersects with the arrangement direction of the plurality of recesses of the upper diffusion sheet closest to the lower prism sheet in the plurality of diffusion sheets with an angle difference of less than 30°. The optical sheet layer as described in claim 1, wherein the aforementioned top angle is less than 120°. The optical sheet layer as described in claim 2, wherein the aforementioned top angle is less than 110°. An optical sheet laminate as described in any one of claims 1 to 3, wherein no other optical sheet exists between the upper diffuser sheet and the lower prism sheet. An optical sheet laminate as described in any one of claims 1 to 3, wherein the plurality of recesses are disposed on the light-emitting surface of the upper diffuser sheet opposite to the lower prism sheet. An optical sheet laminate as recited in any one of claims 1 to 3, wherein the plurality of diffusion sheets include a lower diffusion sheet in which the arrangement direction of the plurality of recesses is different from that of the upper diffusion sheet. A backlight unit is assembled in a liquid crystal display device, and guides light emitted from a plurality of point light sources toward the display screen side; an optical sheet layer as described in any one of claims 1 to 6 is included between the aforementioned display screen and the aforementioned plurality of point light sources; the aforementioned plurality of diffusion sheets are arranged between the aforementioned plurality of point light sources and the aforementioned pair of prism sheets. As described in claim 7, the backlight unit, wherein the aforementioned multiple point light sources are white light sources. A backlight unit as described in claim 7 or 8, wherein the plurality of point light sources are arranged on a reflective sheet disposed on the opposite side of the display screen as viewed from the plurality of diffusion sheets. As described in claim 7 or 8, the distance between the plurality of point light sources and the plurality of light diffusion sheets is less than 5 mm. A liquid crystal display device includes a backlight unit as described in any one of claims 7 to 10, and a liquid crystal display panel. An information device includes a liquid crystal display device as described in claim 11. A method for manufacturing a backlight unit, the backlight unit being assembled in a liquid crystal display device and guiding light emitted from a plurality of point light sources toward a display screen side, the method comprising the following steps: arranging a plurality of diffusion sheets by lamination on the display screen side when observed from the plurality of point light sources, the plurality of diffusion sheets being provided with a plurality of slightly inverted quadrangular pyramid-shaped recesses on at least one side; and arranging a pair of prism sheets whose prism extension directions are orthogonal to each other on the display screen side. The steps of viewing the display screen side from the plurality of diffusion sheets; the top angle of the plurality of concave portions is greater than 95°; the plurality of concave portions are arranged in a two-dimensional matrix; the plurality of diffusion sheets and the pair of prism sheets are arranged so that the prism extension direction of the lower prism sheet close to the plurality of diffusion sheets in the pair of prism sheets and the arrangement direction of the plurality of concave portions of the upper diffusion sheet closest to the lower prism sheet in the plurality of diffusion sheets intersect with an angle difference within 30°.

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